Purpose We determine the prevalence of neutralizing antibodies (NAbs) to adeno-associated virus (AAV) in the vitreous humor and serum of patients with vitreoretinal diseases and investigate the relationship between NAb titers in the vitreous humor and serum. Methods We analyzed NAbs to AAV serotypes 2, 5, 8, and 9 via in vitro neutralization in the vitreous humor and serum from 32 patients requiring vitrectomy for vitreoretinal diseases. The blood–retinal barrier (BRB) was evaluated for integrity based on preoperative examinations, with vitreous hemorrhage (VH) on funduscopy or dye leakage on fluorescein angiography observed indicating disruption. Results NAb levels were much lower in the vitreous humor than in the serum regardless of serotype. Patients with VH had higher levels of NAbs in the vitreous humor than those without VH. The NAb ratio (ratio between NAb titers in the serum and vitreous humor) was much lower in patients with epiretinal membrane with than in those without leakage. A significantly lower NAb ratio was noticed in patients with than in those without BRB disruptions. Conclusions The NAb ratio between levels in serum and vitreous humor varies according to the condition of the BRB. Therefore, in addition to measuring the serum NAb level, physicians should examine BRB integrity when planning retinal gene therapy. Translational Relevance This study provides substantial basis for retinal gene therapy using AAVs and how maintenance of BRB integrity in target diseases should be considered.

In addition to laser photocoagulation, currently used therapeutic interventions for diabetic retinopathy (DR) include relatively short-lived anti-VEGF drugs targeting vascular endothelial growth factor (VEGF). The latter requires frequent administration via intravitreal injections to effect long-term VEGF suppression. However, due to the patient burden associated with this treatment modality, gene therapy may represent a preferable alternative, providing long-lasting yet patient-friendly effects. Here, we explore the therapeutic efficacy of rAAV2-sVEGFRv-1, a recombinant adeno-associated virus encoding a soluble variant of VEGF receptor-1, upon early DR processes. Bevacizumab, an anti-VEGF agent often prescribed off label to treat DR, was used as an experimental comparator. Administered by intravitreal injection to a streptozotocin-induced diabetic mouse model, rAAV2-sVEGFRv-1 was shown to effectively transduce the mouse retinas and express its transgene therein, leading to significant reductions in pericyte loss and retinal cell layer thinning, two processes that play major roles in DR progression. Acellular capillary formation, vascular permeability, and apoptotic activity, the latter being the cell death mechanism by which retinal neurodegeneration occurs, were also shown to be reduced by the therapeutic virus vector. Immunohistochemistry was used to visualize that rAAV2-sVEGFRv-1 has an effect on cell types important to DR pathophysiology, particularly the ganglion cell layer and glial cells. Combined with our previous work showing that the therapeutic virus vector reduces neovascularization, our current results reveal that rAAV2-sVEGFRv-1 addresses the early aspects of DR as well, thereby demonstrating its potential as a human gene therapeutic versus the condition as a whole.